Question

I have a file in *.las format and i wish to count how many points are Return1, Return2,…,Return5
I use a If…Else Statements, but i wish to understand if there is a way more elegant and code saving. Thanks in advance for help and tips.

    Return1 = 0
    Return2 = 0
    Return3 = 0
    Return4 = 0
    Return5 = 0
    count = 0
    for p in lasfile.File(inFile,None,'r'):
        count +=1
        if p.return_number == 1:
            Return1 += 1
        elif p.return_number == 2:
            Return2 += 1
        elif p.return_number == 3:
            Return3 += 1
        elif p.return_number == 4:
            Return4 += 1
        elif p.return_number == 5:
            Return5 += 1

Answer 1

You can use a dict of counters (in this case it can also be a list). defaultdict is quite convenient:

from collections import defaultdict
returns = defaultdict(int)
count = 0
for p in lasfile.File(inFile, None, 'r'):
    count += 1
    returns[p.return_number] += 1

Edit: I’m not sure if DSM is posting a separate answer with Counter examples, so I’m going to reply to the OP’s question here:

@DSM: could i combine Counter? ex: if i wish to count p.return_number and p.scan_angle in the same time – Gianni

Counter will count values in the iterable you give it. The iterable is supposed to be homogenic. For example, if scan_angles can take values of 1, 2, etc., then you can’t use the same Counter for both and get correct results. If the values don’t overlap, you can get correct results, but your code will be confusing and hard to understand. I’d suggest to use two Counter‘s: one for return_numbers and one for scan_angle‘s. You can use the same loop to populate both easily (and the same stands for defaultdict‘s), but if you want to compress creation and filling of two Counter‘s into one statement, you’ll need something like

from collections import Counter
rnc, sac = map(Counter, 
  zip(*((p.return_number, p.scan_angle) for p in lasfile.File(inFile,None,'r'))))

Note that at least on Python 2 it will produce a list, so all data will be held in memory at once at some point.

Yet, the much simpler ways to go are:

• use two defaultdicts:

  returns, angles = defaultdict(int), defaultdict(int)
  for p in lasfile.File(inFile, None, 'r'):
       returns[p.return_number] += 1
       angles[p.scan_angle] += 1
       count += 1
  

• or fill two Counters in two different reads of the file:

  fp = lasfile.File(inFile, None, 'r')
  returns = Counter(p.return_number for p in fp)
  fp = lasfile.File(inFile, None, 'r')
  angles = Counter(p.scan_angle for p in fp)